Natural selection affects frequencies of AG and GT dinucleotides at the 5′ and 3′ ends of exons

GT and AG, located at the 5′ and 3′ ends of introns, are important for correct splicing. It is anticipated that natural selection decreases frequency of AG and GT near the 5′ and 3′ ends of exons, preventing appearance of cryptic splicing sites. The data presented in this article support the expectation.